The present invention relates generally to the field of sanitary centrifugal pumps, and more particularly to a hygienic mechanical seal flushing system for pure liquids in sanitary centrifugal pumps.
Sanitary centrifugal pumps are used for high purity liquids in the pharmaceutical, biotech, food, beverage and chemical industries. Of major concern in these industries are pump cleanliness and the need for continuous sterility. As a result, sanitary centrifugal pumps are typically made of stainless steel or other corrosion resistant materials, are machined instead of cast to eliminate pits, cracks, crevices and porosity, and are often polished to produce a very smooth finish. In addition, sanitary centrifugal pumps are typically part of a larger system of piping, valves, filters and other processing equipment. This equipment requires the ability to be cleaned-in-place or steamed-in-place without substantial disassembly. In addition, the liquid being pumped must be used to cool and flush the mechanical seals, instead of a flushing liquid from an outside source, to ensure that the flushing liquid does not contaminate the liquid being pumped.
Typical prior art flushing systems for sanitary centrifugal pumps use a series of external pipes or tubing, valves, gaskets and connections that are tapped from the outlet port of the pump and routed into the seal cavity to provide a circulation loop of liquid to lubricate and cool the front seal face of the mechanical seal. An additional external recirculation loop can be tapped from the outlet port, the circulation loop, or other areas in the pump housing and routed into an area adjacent the stationary section of the mechanical seal to cool and flush the front and rear seal faces in double mechanical seal applications.
Prior art sanitary pumps with external flushing systems present a number of problems relating to the sterility of the pumps. External piping with bends, elbows, connectors, gaskets, valves, unions, gauges, and flow meters all present possible areas of contamination and are less able to be cleaned-in-place or steamed-in-place effectively. The external piping is also susceptible to damage and subject to vibration and leakage. Further, the external piping must be disassembled for adequate inspection, the bends and elbows must be inspected with borescopes, and reassembly allows for potential errors, contamination, misalignment, and gasket deformation. Great care, in addition, must be taken to install all piping with no horizontal runs or low points, as product may collect in “dead leg” areas not sloped correctly to allow full draining.
The present invention relates to improvements over the sanitary centrifugal pumps and seal flushing systems described above, and to solutions to the problems raised or not solved thereby.